This invention relates to improvements of fiber-reinforced elastic body and a power transmission belt using the same, and in detail relates to measures for extending the running life of the power transmission belt such as a V-ribbed belt and a V-belt under high-temperature atmosphere.
Recently, as the demand on energy conservation, compaction and the like increases, temperature has been increased around an automotive engine room as compared with around a conventional one. Accompanying this, temperature in a use environment of a power transmission belt has been also increased. Conventionally, as material for power transmission belt, there has been mainly used natural rubber, styrene-butadiene rubber, chloroprene rubber or the like. However, power transmission belts using these rubbers generate cracks at their hardened compression rubber layers at an early stage under high-temperature atmosphere.
To eliminate such a phenomenon of early-stage breakage of the power transmission belt, improvements in heat resistance of the chloroprene rubber have been considered so that certain effects have been brought. However, as far as the chloroprene rubber is used, the improvements in heat resistance are limited and sufficient effects have not yet been provided at the present time.
Then, it has been considered to use chlorosulfonated polyethylene rubber having excellent heat resistance as material for power transmission belt. Though the power transmission belt made of chlorosulfonated polyethylene rubber provides largely extended running life and excellent heat resistance under high-temperature atmosphere as compared with the power transmission belt made of chloroprene rubber, it is very inferior in running life under low-temperature atmosphere of less than -30.degree. C. The reason for this is assumed as follows. That is, since the conventional chlorosulfonated polyethylene rubber is formed by chlorosulfonating linear high density polyethylene whose content of chlorine is 35 wt. %, cohesion of chlorine becomes significant thereby causing hardening of rubber in the low-temperature range. This reduces the rubber in elasticity, resulting sin easy-to-break rubber.
To solve the above problem, there is proposed a power transmission belt, in which a linear low density polyethylene rubber composition, chlorosulfonated so as to have the content of chlorine within the range of 15 to 35 wt. % and the content of sulfur within the range of 0.5 to 2.5 wt. %, is used for a compression rubber layer repeatedly subjected to compressive deformation on the belt run and a chloroprene rubber composition or a hydrogenated nitrile rubber composition is used for an adhesion rubber layer (See Japanese Patent Application Laid-Open Gazette No. 4-211748).
Meanwhile, there is a conventional power transmission belt in which cords as fibers for reinforcing rubber are embedded into a rubber part such as the adhesion rubber layer forming the belt. In order to adhere the rubber part to the cords, commonly used is a mixture liquid of a resorcine-formaldehyde initial condensation product and latex (hereinafter, referred to as an RFL liquid).
In this case, the RFL liquid is generally compounded in such a manner that resorcine and formaldehyde are reacted within the initial molecular ratio of 1.0/1.0 to 1.0/3.0 through basic catalyst and then a resorcine-formaldehyde initial condensation product thus reacted and latex are mixed so as to be 10/100 to 30/100 in weight ratio therebetween.
Commonly used as latex is the same type one as the rubber part forming the belt. For example, in the case the rubber part is made of natural rubber or styrene-butadiene copolymer rubber, vinylpyridine-styrene-butadiene terpolymer rubber latex, styrene-butadiene copolymer rubber latex or natural rubber latex is used. In the case the rubber part is made of the chloroprene rubber, chloroprene rubber latex is used. Accordingly, it can be assumed to use chlorosulfonated Polyethylene rubber latex as a latex ingredient for RFL liquid.
However, the inventors have found out that in the conventional methods for compounding an RFL liquid, adhesion cannot be provided between chlorosulfonated polyethylene rubber and fibers.
For example, there is proposed a method for treating fibers with an RFL liquid including NBR (acrylonitrile-butadiene rubber) latex or carboxylated NBR latex, as disclosed in Japanese Patent Application Laid-Open Gazette No 61-127738. In this method, however, since the rubber type is different between the latex and the rubber part, secure adhesion cannot be provided between the rubber part and the fibers.
Further, Japanese Patent Application Laid-Open Gazette No. 5-125200 discloses a method for treating fibers with an RFL liquid having 2,3-dichlorobutadiene-contained polymer (hereinafter, referred to as 2,3-DCB-contained polymer). In this method, polyester fibers are first treated with a treatment liquid (first adhesive) having an isocyanate compound and/or an epoxy compound and then treated with resorcine-formaldehyde latex (second adhesive) having resorcine-formaldehyde resin and 2,3-DCB-contained polymer latex. Thus, polyester fibers are securely adhered to chlorosulfonated polyolefine through vulcanization.
The above method for subjecting polyester fibers to adhesive treatment provides an enhanced static adhesive strength. However, the adhesive strength between the rubber part and the fibers is unstable in the case of power transmission belts subjected to dynamic stimuli thereby readily inviting troubles. It is assumed as the main reason that because 2,3-DCB-contained polymer is very hard, impregnation property of the polymer between filaments of the fibers is unstable.
In view of the foregoing problems, this invention has been made. An object of this invention is to obtain a fiber-reinforced elastic body in which polyester fibers and chlorosulfonated polyolefine are securely adhered therebetween and particularly to obtain an excellent dynamic adhesive strength in a power transmission belt formed of the above fiber-reinforced elastic body.